An isocoumarin derivative, particularly 3-hydroxymethyl-6-methoxy-8-hydroxy-1H-2-benzopyran-1-one represented by the formula ##STR2## was first found as a compound produced by Streptoverticillium eurocidicum, and has attracted attention under the name of the antibiotic MI43-37F11 because of its growth-inhibiting activity against various animal cells and human cancer cells (Japanese Patent Laid-Open No. 2177/'91). Subsequently, investigations have been made on the method for the chemical synthesis of the aforesaid antibiotic MI43-37F11 (hereinafter abbreviated as MI43). As a result, isocoumarin derivatives having a leaving group-containing methyl group (e.g., halomethyl) or benzyloxymethyl at the 3-position of an isocoumarin skeleton have been provided as intermediates (Japanese Patent Laid-Open No. 112884/'92), and isocoumarin derivatives having, at the aforesaid 3-position, a group of the formula ##STR3## wherein R.sub.3 and R.sub.4 are each independently a substituted or unsubstituted alkyl group, an alkoxy group, an alkanoyloxy group, a mono- or di-substituted amino group, a phenylthio group or N.sub.3, have been provided as compound having a pharmacological activity similar to that of MI43 (Japanese Patent Laid-Open No. 97841/'93).
On the other hand, the use of MI43 as an immunological regulator has been proposed because its oral administration can significantly inhibit adjuvant arthritis in rats and collagen-induced arthritis in mice (Japanese Patent Laid-Open No. 183966/'94). Although MI43 is considerably effective as an immunological regulator, there would still remain a need for the provision of a more effective compound or medicine.
In the case of drugs conventionally used for the treatment of autoimmune diseases, such as steroid hormones, gold preparations, D-penicillamine, levamisole and salazosulfapyridine, strict restrictions are encountered in using them, because they may sometimes produce serious side effects such as adrenal dysfunction, infection, renal disorders, hematopoietic disorders and gastrointestinal disorders.
Under the above-described background, an object of the present invention is to provide pharmaceutical preparations having no appreciable side effects and exhibiting excellent efficacy (in particular, bioavailability) in mammals including human beings.